New apple disease spoils even pasteurized foods

ITHACA, N.Y. — New Yorkers love apples. The Empire State is the second-largest apple grower in the U.S. and is the No. 1 producer of processed apple products, such as cider, juice and canned apples.

Given this appreciation for apples, consumers might be concerned by reports from food scientists of a fungus, Paecilomyces niveus, that spoils apple products even after heat pasteurization. The fungus also produces an FDA-regulated toxin called patulin that is found in these spoiled processed foods.

A new study, published online in March in the journal Plant Disease, describes for the first time a new apple disease, Paecilomyces rot, caused by the little-studied fungus. Though food scientists have attributed P. niveus in foods to soil contamination, the study’s authors, doctoral student Megan Biango-Daniels and Cornell Univeristy mycologist Kathie Hodge, now think infected apples may be the true source.

“No one knows how (the mold) gets into apple products,” said Biango-Daniels, who works in Hodge’s lab. “Since it’s known to be in orchard soils and it’s related to other pathogens that attack apples through wounds, I thought that maybe it could infect apples that way, too.”

Created wounds

In the study, the researchers created wounds in Gala and Golden Delicious apples with a toothpick covered with the mold. The apples developed brown rings of rot that resembled other apple diseases, such as black rot, bitter rot and bull’s eye rot.

When they cut the apples open, they found spores of P. niveus being made inside the cores. A cross-section of an infected apple shows the disease makes a U-shaped bruise-like rot.

The researchers found P. niveus in 34 percent of soils sampled from apple orchards across New York.

“It’s a really tough mold,” said Hodge, associate professor in the School of Integrative Plant Science. The fungus produces abundant, durable ascospores that can survive heat as high as 194 degrees.

Bad apples

This leads to spoilage on the shelf of even pasteurized processed foods containing bad apples. The disease may be overlooked because it so closely resembles other apple diseases, Biango-Daniels said.

“The most effective way we can prevent apple spoilage from this mold is to cull apples with wounds and bruises that makes them likely to get this, and to never use dropped apples, the ones that people pick up off the ground,” Biango-Daniels said, adding she doesn’t yet know of a way to stop spoilage once the fungus has been introduced in foods.

Researchers will now make processed apple products, pasteurize them and see if the fungus survives when bad apples are used.

“It’s important to think about food spoilage as a continuum and to think about where problems arise and how the whole food system is connected to the end product,” she added.

This work was supported by the U.S. Department of Agriculture National Institute of Food and Agriculture Hatch grant and by a Cornell College of Agriculture and Life Sciences Arthur Boller Apple Research Grant.